The regulation of cellular responses to ischemic, excitotoxic, pathogenic or chemotoxic stresses in the central and peripheral nervous systems (CNS and PNS, repectively), including for example, the brain, the spinal cord, the eye, and the peripheral sensory and motor neurons, is a major frontier of modem medicine. Neurons are non-proliferating cells whose progressive or abrupt loss can result in diseases exemplified by Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic laterial sclerosis (“ALS” or “Lou Gehrig's disease”), and stroke. These diseases and disorders are individually or collectively referred to herein as “central neurodegenerative diseases.” Selected symptoms resulting from these diseases include memory loss, loss of cognitive function, loss of gross and fine motor control, and blindness. Peripheral neuronal loss or neurite damage results in sensory loss exemplified by pain or discomfort, sensorimotor defects, and paralysis.
The incidence of central neurodegenerative diseases increases with age. For example, less than 5% of the population under the age of 65 displays signs of AD. An exponential increase is observed over the age of 65, with as much as 47% of the population displaying some form of AD over the age of 85. Many factors (etiological agents) are responsible for the initiation of neurodegenerative conditions, factors as varied as genetic DNA damage or loss in the mitochondria, abnormal amyloid processing, oxidative stress following ischemia and reperfusion, and loss of neurotrophic support for the nerve cells. The mode of action ultimately underlying such irreversible neuronal loss involves programmed cell death, or apoptosis. Preventing neuronal apoptosis and neurite disfunction represents a new, broad-spectrum, approach to the treatment of progressive central neurological disorders Various other neurodegenerative diseases related to the peripheral nervous system, herein referred to as “peripheral neuropathies”, are characterized by the loss of feeling, experiencing pain, and even paralysis of or in the extremities. These peripheral neuropathies result from disease states such as ALS, Multiple Sclerosis, AIDS, diabetes, and various neuropathies induced by chemotherapeutic treatments such as cisplatin, vinblastine and taxane (Taxol™ and Taxotere™) treatment for cancer therapy, and D4T for the treatment of HIV (Human Insufficiency Virus). In most of these cases, progressive loss of axonal finction occurs initially, resulting in severe symptoms, followed by the apoptotic loss of the neuron. In these cases, inhibiting neuronal apoptosis and or axonal degradation is a new approach to treating these diseases.
A recently discovered family of genes, known as the IAPs (Inhibitor of Apoptosis Proteins), potently inhibit apoptosis in most mammalian cell lines. Members of the LAP family, specifically NAIP, HIAP1,2 and XLIP, are used as survival factors by both neurons and cancer cells to resist intrinsic apoptosis.
NAIP's (Neuronal Apoptosis Inhibitory Protein) primary finction appears to be the regulation of neuronal apoptosis (Xu, D. G. et al. Nature Medicine 1997, 3, 997). NAIP is primarily expressed in neurons where it serves to protect these post-mitotic cells against environmental and metabolic stresses that lead to premature apoptosis of the neuron. Indeed, deletions in the NAIP gene were found to be causally related to the severity of the childhood genetic neuromuscular disease, Spinal Muscular Atrophy (SMA).
Enhancement of NAIP expression in the brain was achieved through the systemic in vivo administration of a neuroprotective alkaloid, K252a (for the isolation and identification of K252a see Sezaki, M. J Antibiot. 1986, 39, 1066, U.S. Pat. No. 6,020,127). In vivo studies demonstrated increased expression of NAIP in hippocampal neurons after K252a administration to rats. These results correlate well with increased protection to ischemic insults provided by this compound (see Xu, D. G. et al. Nature Medicine 1997, 3, 997). Knock-out mice lacking the expression of NAIP displayed dramatic neuronal sensitivity to such ischemic insults.
The exact mechanism by which K252a upregulates NAIP gene expression is not known. However, it is known that K252a inhibits several classes of protein kinases. The X-ray crystal structure of a closely related natural product alkaloid, staurosporine, when bound to the protein kinases CDK2 and cAPK confirmed that staurosporine acts as a competitive inhibitor for the conserved binding site of adenosine triphosphate (ATP), which is found in all known protein kinases enzymes (for a review see Toledo and Lydon Structure 1997, 5, 1551). Several groups have suggested that K252a and its structural analogues, the indolocarbazoles, also bind to the ATP binding site of various protein kinases. A large number of natural products related to the K252a structure (indolocarbazoles) also inhibit various serine-threonine protein kinases. Most of these compounds have undesirable neuronal cytotoxic effects due to their lack of kinase specificity. Non-specific kinase inhibitory compounds can interrupt the neuronal survival signaling pathways for example, by inhibiting PKB or PKC. In fact, protein kinase deregulation has been implicated as a contributing factor to various neurodegenerative disorders (Bradshaw, D. et al. Agents and Actions 1993,38, 137; Knusel B. & Hefti F. J. Neurochem. 1992, 59, 1987). This class of compounds is typified by the following compounds:

K252a displays significant neuronal cytotoxicity at moderate doses in vitro which preclude the measurement of upregulation of NAIP gene expression as a true indication of its neuroprotective mechanism in either cultured neuroblastoma cells or cerebellar granule neurons (CGN). These findings suggest that highly specific compounds will be required in order to have pharmaceutical potential in regulating pro-apoptotic action in various diseases.
Various cancers and cell lines, including colon, lung, and breast, display elevated levels of other IAPs, including HIAP1,2 and XIAP, as either mRNA and/or protein (U.S. Pat. No. 5,919,912). Scientist at Aegera Therapeutics Inc. have shown that the down-regulation of the ILAPs in cancer cells can effectively shift the chemotherapeutic dose response required to kill such cancer cells, in the case of HAIP1, or to kill cancer cells outright, in the case of XIAP (US pat application. Compounds that down-regulate the expression of these genes would therefore be useful in treating cancers. In several cases, the cytotoxic properties of the indolocarbazoles have been exploited to affect a therapeutic use in cancer eg. Staurosporine, UNC 01, Rebeccamycin and NB 506 amongst others. Specifically, UNC 01 down regulates XIAP expression in B-cell chronic lymphocytic leukemia cell lines, inducing apoptosis (Kitada, S. et al Blood 2000, 96, 393).
Indolocarbazole Alkaloids Staurosporine and K252a
Various derivatives of the natural products Staurosporine and K252a have been described for the treatment of neurodegenerative disorders. U.S. Pat. No. 6,013,646 to Roderet al. (issued Jan. 11, 2000) discloses K252a derivatives incorporating a carbon at the tetrahydrofuran oxygen position of the K252a sugar moiety prevents tau hyperphosphorylation by the direct inhibition of the ERK family of protein kinases, also known as the MAP kinases. Tau hyperphosphorylation results in the destabilization of regular microtubular organization and the formation of neurofibular tangles (Iqbal, K. et al. FEBS Lett., 1994, 349, 104; Garver, T. D. et al., J. Neurosci. Res., 1996, 44, 12). Neurofibulary tangles are associated with neurodegenerative diseases such as AD and PD. A report by Murakata, C. et al. (J. Med Chem. 1997, 40, 1863) established that the semisynthetic K252a analogue, CEP 1347, is a selective neurotrophic agent in which the undesirable TrkA and PKC inhibitory activities have been reduced, as demonstrated in a ChAt assay. Additionally, this class of compounds appears to inhibit the production of TNF-α (tumour necrosis factor), which is intimately involved in the initiation of neuronal apoptosis. At the same time CEP 1347 and related compounds upregulated the production of IL-1β (Mallamo et al, WO96/31515; Hudkins et al, WO 97/46565; Engber et al, WO97/49406). Maroney, A. C. et al. showed that CEP 1347 inhibited JNK1 activation (J. Neurosci., 1998, 18, 104).
Other indolocarbazole derivatives are disclosed by Glicksman, M. A. et aL (WO 95 07911), Lewis, M. E. (WO 94 02488), Lewis, M. E. et al. (U.S. Pat. No. 5,756,494, No. 5,741,808, and No. 5,621,101). Indolocarbazole derivatives have also been reported for use in treatment of cancer (EP 0 323 171, EP 0 643 966, U.S. Pat. No. 4,923,986, U.S. Pat. No. 4,877,776, WO 94 27982), as antimicrobial agents (Prudhomme et al, J. Antibiotics, 1994, 47, 792) and in the treatment of hypertension (Hachisu et al. Life Sciences 1989, 44, 1351).
A variety of synthetic procedures have been reported in the literature for the preparation of bis(indolyl)pyrrole-2,5-diones and indolocarbazoles. See, for example, Bit et al., J. Med. Chem., 1993, 63, 21; Bergman et al., Tetrahedron Lett., 1987,28, 4441; Davis et al., Tetrahedron Lett., 1990, 31, 2353, 5201; Faul, M. M. et al., Tetrahedron Lett, 1999, 40, 1109; Faul M M. et al. U.S. Pat. Nos. 5,859,261, 5,919,946, and 6,037,475. For a general review of the chemistry and properties of these alkaloids see Gribble, G. W.; Berthel, S. J. “Studies in Natural Products Chemistry”, 1993, 12, 365. For synthetic studies see Wood, J. L. et al. J. Am. Chem. Soc. 1997, 119, 9641; and Danishefsky, S. et al J. Am. Chem. Soc. 1996, 118, 2825.
A class of indolocarbazoles having fused imidazolyl ring systems are known as the granulatimides. Iso-granulatimide has been shown to be an effective G2 check point inhibitor in p53 deficient cancer cell lines, suggesting its potential in cancer chemotherapy (PCT WO99/47522, Sep. 23 1999). Some members of this class are illustrated below.
Pyrrolo-β-Carbazole Derivatives.
Compound “a”, below, represents a typical intermediate in the synthesis of certain disclosed pyrrolo-β-carboline compounds, and was reported by Davis et al. (J. Med. Chem., 1992, 35, 177) as an inhibitor of PKC. This compound was prepared using a different chemistry than that of the instant invention, and has not been further elaborated or cyclized.

Compound “b”, above, has been proposed as an undesirable, unstable intermediate in the synthesis of staurosporine aglycone. The compound was not isolated or further elaborated (Wood, J. L. et al., J. Am. Chem. Soc., 1997, 119, 9641).
A variety of synthetic procedures have been reported in the literature for the preparation of 3-(1H-indol-3-yl)-1H-pyrrole-2,5-diones involving the condensation of indole with maleimide (Bergman, J. et al. Tetrahedron, 1999, 55). Most of these synthetic procedures have distinct limitations with regards to the use of harsh reaction conditions, thereby limiting the functional groups tolerated during the coupling reactions, the need for protection of the pyrrole-2,5-dione nitrogen, and the total number of synthetic steps required for the preparation of the desired indolocarbazole nuclei.